GASIFICATION OF LOW CALORIFIC VALUE SOLID FUELS TO PRODUCE ELECTRIC ENERGY

Abstract: An original method for utilization of solid fuels of low calorific value in the production of electrical energy is described which leads to 3 times higher yields than these obtained today by burning in an operation working with efficient complete internal pollution control. The method covers solid fuels of low calorific values 800 to 3.000 Kcal/Kg which pyrolyse by 30 % to 80 % at temperatures under 600 DEG C which are utilized in an operation consisting of two pressure reactors in series the first of fluidized bed type where the pyrolysis is perfomed at 450-600 DEG C which is a reductive process forming hydrogen sulfide and a second pressure reactor of solid bed type where the carbon residue of pyrolysis is directed to be gasified with oxygen or with oxygen-steam where the sulfur is oxidized to sulfur dioxide. The two gas steams are mixed under conditions to neutralize the contained sulfur gases by a Claus reaction: 2H2S + SO2 -> 3S + 2H2O. The fuel gases are produced at temperatures of 600-800 DEG C and at pressures of 20 to 30 atm and are utilized in an external turbine to produce electricity from the thermomechanical energy contained or are exchanged to produce pressure steam. Then the fuel gases are used in a combined circle arrangement to produce electric energy by utilizing their thermal values.

Description: GASIFICATION OF LOW CALORIFIC VALUE SOLID FUELS TO PRODUCE ELECTRIC ENERGY 5. Inventor: GEORGE VALKANAS The invention describes an original gasification method of low calorific value solid fuels e.g. lignites and peats with pyrolysis and oxygen or 10. oxygen-steam gasification in two stages. Additionally it describes an original process by which the gases produced are utilised in a Co-Gas advanced system for producing high amounts of electric energy in an operation running without 15. environmental pollution. With the existing crisis in securing adequate amounts of energy and since petroleum supplies are not regular in availability and price, the national 20. programmes for producing electric energy rather prefer to develop local energy sources. In this preferred development, coal is the main source to consider which is the first fuel to be used in power production and is more abudent and 25. more regularly distributed in the World than oil. The resources in coal are divided in low and high thermal value. They are also divided according to their sulfur content which by burning the solid fuels becomes sulfur dioxide creating toxic environmental pollution. With that problem, the utilisation of solid fuels is restricted to those containing low 5. sulfur and create as low as possible environmental damage. In relation to coal and to its utilisation in the production of electric energy it is observed that by 10. its burning, the result in electric energy is low, it releases high amounts of sulfur dioxide, fly ash and nitric oxides and it creates high corrosion in the equipment. Additionally, by burning solid fuels high amounts of 15. carbon dioxide are produced which today are considered a major pollution factor, being the main source for the green-house conditions emerging in our Planet. And all these environmental and production problems appear more critical by the use of solid 20. fuels of low calorific values such as lignites and peats. To face these problems today there exist solutions leading to the reduction of the sulfur content in those low calorific fuels and to the neutralisation 25. of the combustion gases. Those solutions, however, are costly and the corrections offered, because of cost, do not make them attractive. A better approach appears to be the gasification of those low calorific fuels as an action attractive today in spite of its leading to high losses of energy. With total gasification the gases can be washed to separate them from the toxic gases and the flying ash but with total gasification the thermal value is further reduced to 65-70* and expensive industrial installations are needed in the operation. 10 In the meantime, however, with the development of gas turbines in the production of power more economical solutions are available to utilise gases. Our original solution is such a method which utilises the 15. fuel gases produced in Co-Gas advanced systems by which the degree of produced electric energy with the use of air turbines and combined cycle is improved. For operating the gas turbines, however, we need fuel gases free of corrosive and free of tars and liquid 20. byproducts, but also of the highest possible thermal value. Considering those developments, the technological characteristics of lignites and peats of low calorific value have been studied in the described 25. invention and it has been discovered that those solid fuels either as they are received or after deashing (described in another invention) show high efficiency in running in such an advanced system for producing electric energy because those fuels are pyrolysed at high extent (40-85%), highly exothermally without forming tars and liquid byproducts. The pyrolysis of 5. those low calorific value fuels is optimised at 400-600 * C, and the pyrolytic treatment is highly exothermic in character. The pyrolysis residue is received in high carbon purity with thermal value of 4.000-6.000 Kcal/Kg without ash, or with 2.200-4000 10. Kcal/Kg with ash. It has been studied for the described invention the gasification of that carbon residue with oxygen and preferably with oxygen-steam and has been discovered that the fuel gases produced are of extremely high thermal value and 15. received at high temperatures of 900-1.000'C and that the gasification achieves the complete utilisation of carbon. According to this procedure it has been discovered for the said invention that the two-stage gasification of lignites and peats achieves a very 20. high high thermal efficiency, and the oxidative gasification does not lead to tars or liquid byproducts. It has been discovered for the said invention that 25. the pyrolytic treatment proceeds exothermally producing 350-600 Kcal/Kg at 600 * C and the exothermic output in energy is related to the degree of py rol y sis. To that quantity of energy is a dd ed the thermal content of the fuel gases and the thermal exchan g e of the bottom ash and the fuel gases p roduced in the oxidative gasification. 5. More heatin g needs can be adopted on the incoming solid fuels as shown in diagram 1. Thus, the conditions b y which the thermal balance of the p yrolytic treatment is covered without using carbon thermal ener gy have been also studied. And this 10. leads to high energy economy and to high energy utilisation of the low calorific solid fuels. The two sta g es of gasification, the pyrolysis treatment and the gasification proper (with oxygen or with oxy g en-steam) have been discovered through the 15. described invention that beneficially lead to p roducts of different chemical character in that the py rol y sis is a reductive treatment in which sulfur is g asified as h y drogen sulfide and the oxidative treatment is oxidative in chemical character and the 20. sulfur g asified is taken as sulfur dioxide. Then it has been searched and worked out a solution for neutralisin g those sulfur gases by creating conditions to run the fuel gases to a Claus reactor. With mixin g those fuel streams, after first 25. utilisation of their thermomechanic l energy in a turbine system, with temperatures of 600 # C and at a pressure of 30 at. and feeding them to a Claus catalytic reactor the sulfur gases release product sulfur 2 H 3 S + S0 2 > 3S + 20H 2 5. That possibility to neutralise the sulfur gases beneficially simply with production of valuable sulfur is the main key in that invention in riginality and in importance since it satisfies 10. the first goal to this R & D involvement, which was to possibly develop a method of producing electric energy from low calorific value solid fuels which does not create toxical pollution problems from sulfur dioxide and from flying ash. The derived 15. sulfur is collected in high purity and may in small amounts be taken with the gases flow from where it is washed with water and collected. Another originality of the said invention is that the 20. fuel gases are received to pressure of 30 at. developed during the pyrolytic treatment and makes a working pressure in the two gasification treatments and in the Claus unit. The fuel gases are received at temperatures of 600 * to 900'C and at pressure 30 at., 25. free of corrosive substances and sulfur gases. Another basic original result of the said invention is the experimentally proved evidence that the low calorific value solid fuels (lignites and peats) are pyrolysed exothermally because of the oxygen content of the organic materials, which resemble wood. Wood 5. and woody biomass is known that it pyrolyses exothermally at temperatures higher than 400oC and that has been utilised beneficially in the past at the distillation treatment of wood and recently in the pyrolytic treatment of garbage biomass. The low 10. calorific value solid fuels (lignites and peats) have the following woody consistency. T A B L E 1 15. The consistency of Lignites and Peats Constituents Lignites Peats pH 5,8 - 6,9 4,6 - 5.4 20. Ash 15 - 35 6 - 20,5 Waxy substances etc. 5,2 - 6,8 8,1 - 8,3 Humic acids 20 - 33.8 18 - 34.1 Humins 30 - 40 37 - 42,1 Holocellulose 31 - 35 26.1 - 32.9 25. d-cellulose 8 - 15 10.5 - 12,0 With the above which determine the nature of the pyrolyric tendency and the result of the gasification with oxygen or with oxygen and steam a system is formed with profitable thermal balance in thermal exchanges and final results. The thermal operational 5. parameters determine: a. That the heating of the solid fuels to the pyrolytic treatment is affected by the rejected thermal energy, that is thermal energy from 10. off-gases, bottom ash, etc. b. That the pyrolytic gasification is exothermic, producing 250-600 Kcal/Kg thermal energy with formation of operational pressures up to 30 atm. 15. and it is advanced without being influenced by moisture or ash presence and it is a reaction of reductive chemical character. c. That the Claus reaction of neutralising the 20. sulfur gases is spontaneous at temperatures 600 * C and at pressures of 30 at. of the fuel gases and provided that the molar ratio of H2S/S02 is 2:1. the reaction is quantitive. d. That the installation for utilising the 25. procedure should operate under pressure 30 at. and at temperature of fuel gases up to 900*C. The drying of the solid fuels e.g. lignites or peats as they are or after a deashing treatment is adopted on pulverised form, first with mechanical dewatering and then with heating to 180-300*C with exchange of 5. the ash thermal energy received at 1.000'C and of the thermal energy of the off-gases so that to be finally received as off gases at 180-300'C. The pyrolytic treatment starts with the solid fuel 10. e.g lignite at temperature 180-300*. while to be pyrolysed. temperatures of 450 to 600 * are needed. To form those temperatures the following thermal sources are used a) that of exchange on the gases of the oxidative gasification which are received at 1000'C 15. and can offer 200 * C to the pyrolysis mass (cooled down to 600 * C) and b) that of the thermal energy resulting from the exothermal pyrolytic reaction which will increase temperatures by 200* to 300*C. With those thermal offers the pyrolytic treatment 20. attains temperatures of 600*C and higher. The energy coverage of the pyrolytic treatment is controlled by heating arrangements on the incoming lignite if needed, nevertheless, this is depending largely on the relative extent of the pyrolysis and of the 25. oxidative gasification treatments. The gasification of the carbon pyrolysis residue with oxygen or preferably with oxygen steam like is added at 600 * C with high carbon purity and in porous stage is proceeding very energetically with quantitative transformation of the contained carbon and rapid increase of the temperature to 900*-1000*C. The 5. losses in thermal energy at the oxidative treatment are comparably low, lower than 12% and this refers to the 50% of total. The actual thermal energy loss is under 6% which is low for total gasification treatment and a high energy benefit. 10. The two streams of gasses the one from pyrolysis and the one from gasification with oxygen or with oxygen steam are mixed as they are received or after energy exchange utilisation in a turbine. They are then 15. directed to the Claus unit which operates under pressure. In the Claus unit the sulfur gases are neutralised and the fuel stream is received free of corrosive gases. 20. The analysis of gases produced in the two reactors that of pyrolysis and that of oxygen gasification for a number of greek lignites and peats are given in the following Table 2 as maxima and as minima of composition. 25. T A B L E 2 The composition of the gas fuels from pyrolysis and oxygen gasification From Pyrolysis, % From Oxygen Gasification, % Methane 20-35% 10. Carbon monoxide 30-50% Carbon monoxide 35-40% Carbon dioxide 2-6% Carbon dioxide 16-22% Hydrogen 16-22% Hydrogen 40-60% 15, Hydrolgen Sulfide 1-3% Sulfur dioxide 1-2% The procedure of the pyrolytic reaction on a number of solid fuels of low thermal value gave the results of Table 3 T A B L E 3 The pyrolytic reaction of low caloric value lignites and peats in % (free of ash and in dry form) 25. tem p erature Peat Ptole ais Megalopolis Aliveri ( North (Peloponessus, (Euboea, Greece) Greece) Greece) 5. 400 * 15,2% 17,3% 35,4% 16,8% 450 * 22,4 23,5 44,3 23.4 500 * 34,24 35,28 52,4 37,2 550 * 34,48 39,43 67,42 44,64 600 * 44,00 44,24 75,42 51,00 10. 650 * 44.63 46,6 79,38 56,00 Ash content 11,55% 10,8% 20,6% 11.5% Kcal/Kg of the solid fuel 4.400 5.100 4.400 5.400 15. Kcal/Kg of the coal residue 4.465 5.200 4.020 5.730 In the procedure diagram showing the flow of utilisation of the gases produced for electricity p roduction are easily recognised the originalities 20. and the energy benefits obtained according to the described invention. The production sequence consists of two pressure reactors in series that of pyrolysis and that of 25. gasification with oxygen. The pyrolysis reactor is designed to operate at temperature of 700* and pressure of 50 atm and is of fluidised bed type with automated systems for carbon feeding, and for withdrawing the products obtained: the carbon residue and the fuel gases. The gasification reactor is designed to operate at 5. temperatures up to 1200 * and at pressures up to 50 atm and it is of solid bed type with automated systems for feeding and introducing oxygen and for releasing ash and the gases produced. 10. Another possibility for applying the said invention a combination of the pyrolytic treatment with burning the carboneous residue in the existing boiler producing pressure steam. According to this solution the solid fuels e.g. 15. lignites or peats are introduced to the pyrolysis reactor with moisture up to 60% or in dry or semidried form and the fuel gases produced are fed to a turbine for utilisation of their thermomechanical energy then are washed and the hydrogen sulfide 20. present is neutralised by known procedures such as in a combination with the Stretford process. The fuel gases after this are burned to produce high amounts of electric energy in a combined-circle advanced system. The carboneous residue in this case is burned 25. in the existing boiler to produce pressure steam to run existing steam turbine or newly installed. With that solution the electric energy output is about three times higher than the one obtained today and the desulfurisation is covering the 70% of sulfur total presence in the solid fuel. 5. In the frame of the described invention it has been invented and proved in practice that the pyrolytic treatment is not influenced by the moisture of ash presence and that this treatment makes an energetic transformation pattern because the energy use is 10. taken by the products produced, the gases and the carbon residue, and the steam formed actually increases substantially the gas volume and their energy content. Apart from utilizing the solid fuel optimized by biorefining release the exothermic 15. reaction is a substantial contribution in energy quantity and as energy source. The fuel gases from the reactors are mixed and directed to a turbine to release part of the 20. thermomechanical energy as electrical energy and then are introduced to Claus reaction unit. In the Claus unit the gases for optimization should have a temperature of 400-450 and a working pressure. The thermomechanical energy can be also used in steam 25. generation by thermal exchange. At the end the fuel gases contain thermal energy up to 95%+ of thermal energy of the initial solid fuel in biorefining utilization and in exothermic reaction energy addition. The fuel gases are fed into an advanced combined 5. circle utilization for electric energy output. This, according to this invention, can exceed the 65% in combination of the turbine for thermomechanic l energy utilization. The yield in electrical energy today is 1,1 Kg of 10. 3.000 Kcal lignite per KWh or with lignites and peats of thermal content 800-1200 Kcal/Kg the yield is 1.8-4.1 Kg/KW of electric energy. With the described invention the yield in electricity is impressively high. 0.41-0,62 Kg of lignite or peat/KWh since the 15. lignites and the peats of low calorific content are utilized according to their energy content in dry form and additionally by the contribution of a sizable exothermic reaction which adds 20-30% in energy increase. After the above conclusion is shown 20. that the described invention in utilizing low caloric solid fuels with pyrolytic tendency of 30% to 80% advances high yields in electricity production which is comparable to solid fuels of high thermal value and to oil, in an operation beneficially running 25. entirely pollution free. The described invention, therefore, introduces a procedure for electricity production of low cost from low calorific solid fuels which have a wide distribution in all the World in an operation which although it produces high amounts of electricity also introduces an operation running free of pollution from flying ash and from S02 and can be arranged also to be free of nitric oxides, thus to be entirely pollution free. Also leads to visable reduction of C02 release 75% per production unit.

Claims: CLAIMS After the description of the invention and the examples and the drawings which determine it, it is 5. claimed: 1. Method of utilization of solid fuels of low calorific value by which those fuels pyrolyse by 40-80% of their carbon part and subsequently the 10. remaining part is gasified with oxygen or with oxygen-steam or burned without formation at all of tarry or liquid byproducts, with overall high thermal balance, with internal pollution control and with production of fuel gases in quality and 15. in quantity to be used in an advanced Co-Gas producing electric energy system. 2. Method of utilization of solid fuels of low calorific value according to claim 1 by which 20. the pyrolytic treatment is reductive in character and the gasified sulfur is taken as hydrogen sulfide. The gasification of the rest is oxidative in character and the two gas streams are mixed at conditions to operate 25. efficiently in the Claus reaction by which the sulfur gases are neutralized forming quantitatively molecular sulfur. 2H a S + S0 2 > 3S + 2H a 0 3. Method by which the pyrolytic treatment is advanced at 450-600 * and operates intensively 5. exothermally producing 250-600 Kcal/Kg of lignite or peat, in relation to the degree of pyrolysis and creates conditions for operation under pressure. 10. 4. Method by which the gasification with oxygen or with oxygen-steam on the pyrolysis Carbon residue it is performed on material at temperature 600 * C, in dry form and at high purity and surface activity so that the 15. oxidation treatment is advanced rapidly with low consumption of thermal energy with formation of high temperatures up to 1.100'C or that carbon residue is burned to produce effectively pressure steam. 20. 5. Method of pyrolysis and gasification in two stages by which the solid fuels of low caloric values which can pyrolyse at extent 40% and higher which contain moisture up to 60% are thermally improved since the pyrolytic treatment 25. operates as an effective dewatering procedure. 6. Method according to the claims 1,2,3,4 and 5 by which the pyrolytic reaction which operates at temperatures of 450-600 * is covered in thermal energy by the exothermic reaction giving 200-300 * , by exchange on the gasification gases 5. which can give 200 * temperature rise and by the thermal energy contained in the incoming solid fuels of 180-3200, also by heating if necessary. 7. Method by which the solid fuels which enter the 10. pyrolysis treatment are dried in pulverized form by exchanging thermal energy with the off-gases and with the bottom ash by which the incoming lignite attains temperatures of 180* to 320 * and is dewatered by 60% to 90%. 15. 8. Method according to the claims 3,4,5 and 6 by which conditions of high energy economy are created since the pyrolysis is covered with rejected form of thermal energy and the 20. gasification with oxygen or oxygen steam is consuming only 6% of carbon in such a way that the total thermal output is very high up to 95% of the content of the incoming solid fuel which with the exothermic reaction contribution gives 25. an energy gain more than 100% on the basic thermal content. 9. Method according to the previous claims by which the solid fuels of low caloric value which are pyrolysed more than 40% after gasification in two stages that of pyrolysis and that of 5. gasification on the carbon residue by oxygen or oxygen-steam are produced fuel gases which in a Claus reaction are easily and beneficially cleaned from sulfur gases contained and are produced with temperatures of 600 * to 800 * and 10. with pressures of 20 to 30 atm that is with high thermomechanical energy content, are then fed on a turbine to produce amounts of electricity from that energy. 10. Method according to the previous claims and 15. specially to claim 9 by which the fuel gases after their utilization and after operation of the Claus reaction and washed with water and then are fed in a combined circle arrangement to produce energy exceeding the 50% of thermal 20. content of the gases. 11. Method by which with utilization of the fuels of low caloric value in a process of pyrolysis and gasification in two stages which leads to 25. internal pollution control and to at least doubling in electric energy production of what is produced today by burning this leads to at least 75% per production unit in lowering the carbon dioxide emission which makes and important result, in facing the pollution problem of greenhouses. 5. 12. Method according to claims 1 to 10 by which the solid fuels of low caloric value are gasified with pyrolysis and gasification with oxygen or oxygen-steam in two stages the gas 10. streams are received at temperatures 600-800* and at pressures of 20 to 30 atm and are neutralized from contained sulfur gases on a Claus reaction unit. The fuel gases are fed in a turbine to utilize their thermomechanical energy 15. and then are used as fuels in a combined circle arrangement by which the electricity produced is 55% to 75% on the thermal value of the incoming solid fuel, with operation of the thermoelectrical unit without pollution damages, 20. without formation of sulfur gases, or flying ash (and by arrangement of nitric oxides) and by reducing the carbon dioxide emission by 75% per production unit.

Inventors: VALKANAS GEORGE N, VALKANAS, GEORGE, N.
Applicants: BIOKAT CORP, VALKANAS GEORGE N, BIOKAT CORPORATION, VALKANAS, GEORGE, N.
Application year: 1994
Main classification: C10J3
IPC codes: C10J3, F01K23